I just picked a '84 K10 short bed that's needs some TLC. I have heat through the vents on the front of the dash whether the selector is set to "off" or another setting. I'd swear I read somewhere that the vacuum source for the heat selector came from somewhere on the AC. The truck had AC but it was removed. I would very much appreciate any help that could be provided. I live in Ohio so defrost is an absolute must.